This invention relates to a system for automatically carrying out the registration of picture images obtained on the basis of picture signals from different image pickup devices of a color television camera.
As image pickup systems for color televisions, there have heretofore been employed extensively an image pickup system equipped with a plurality of image pickup devices, for example pickup tubes having different spectral sensitivity characteristics so as to combine picture signals obtained from the plurality of pickup tubes into a composite color picture signal. In image pickup systems of the above type, it is necessary to accurately carry out the superposition, in other words, registration of picture images obtained on the basis of picture signals from the plurality of pickup tubes.
The above registration may generally be effected by the size control, that is to make the scanned area of an optical image to be picked up by each image pickup device coincided, the correction of geometrical distortion developed by variations in the optical pickup unit and image pickup unit, the centering operation to align the relative positions of scanned areas, and the like. As a system for effecting the aforementioned registration, such a manual registration system as shown in FIG. 1 has been principally relied upon.
In FIG. 1, numerals 1, 2 and 3 indicate respectively a G(green) channel image pickup system, R(red) channel image pickup system and B(blue) channel image pickup system. There is shown at numeral 4 a view finder (or monitor). Designated at numerals 2v, 3v are respectively knob units for effecting the registration. The operator manipulates the knob units 2v, 3v anytime whenever needed while watching picture images in the view finder 4 so as to bring the R and B picture images into registration with the reference picture image, G picture image.
The above prior art system is accompanied by such drawbacks that it is complex and cumbersome to operate and requires considerably long time for adjustment.
The aforementioned conventional registration system is susceptible of developing color variations notably when the use conditions of television cameras change. Among such use conditions, the surrounding temperature is predominant and its variations frequently lead to objectionable color variations, thereby requiring frequent readjustment while using television cameras. Accordingly, the aforementioned manual registration system does not permit satisfactory registration and is unable to provide picture signals of excellent quality.
With a view toward solving the above-mentioned drawbacks of the prior art registration system, so-called autoregistration systems have been proposed and actually employed on a large scale so as to effect the registration automatically whenever it is needed.
An example of such autoregistration systems are shown in FIG. 2, in which numerals 1-3 indicate image pickup systems of different channels as in FIG. 1. Designated at numeral 5 is a test pattern for registration. Numerals 6, 7 are preprocessing circuits while binarization circuits are shown at numerals 8, 9. Intermediate processing circuits are shown at numerals 10, 11. Designated at numeral 12 is a pulse comparator. Numerals 13 and 14 indicate respectively a postprocessing circuit and control circuit. Registration correction units are indicated respectively at numerals 15, 16. Numeral 17 designates a double throw switch.
The test pattern 5 bears thereon a special pattern suitable for registration and is included in the optical pickup unit for the image pickup systems 1-3 of the three channels. The optical pickup unit is constructed in such a way that the pattern 5 is projected on the targets of the image pickup systems 1-3 only when the registration is effected.
The preprocessing circuits 6, 7 are circuits to perform processing of signals such as non-linear amplification and signal clamping (in order to ensure their binarization).
The binarization circuits 8, 9 each outputs a signal "0" or "1" depending on each signal to be fed thereto.
The intermediate processing circuits 10, 11 are circuits to perform operational processing which is required for pulse comparison.
The pulse comparator 12 compares a pulse input through one channel with another pulse input through another channel so as to determine the interval between the former and latter channels and then to output a signal representing the off-set in registration.
The postprocessing circuit 13 serves to perform such processing as error checking or the like.
The control circuit 14 delivers a control signal to a registration correction unit 15 or 16 in accordance with the signal representing the off-set in registration, whereby bringing the image pickup system 2 or 3 into registration with the G-channel image pickup system 1. The control circuit 1 may be formed of a microcomputer or the like.
The double throw switch 17 changes the R-channel registration to the B-channel registration and vice versa.
Operation of the above autoregistration system will next be described. When effecting the registration, the test pattern 5 is advanced into the light path of the optical pickup unit and the resulting pattern images are projected respectively on the targets of the image pickup systems 1-3 of the different channels.
Then, a picture signal of the test pattern 5 obtained from the G-channel image pickup system 1 is input through the preprocessing circuit 6 to the binarization circuit 8, and, after wave-shaped into a pulse-like form at the intermediate processing circuit 10, delivered as a pulse-shaped picture image to the pulse comparator 12.
On the other hand, supposing that the double throw switch 17 has been changed over to the R-channel side as illustrated in the drawing, a picture signal of the test pattern 5 obtained by the R-channel image pickup system 2 is passed through the preprocessing circuit 7 and binarization circuit 9 to the intermediate processing circuit 11, where the picture signal is wave-shaped into a pulse-like form, and then fed to the pulse comparator 12 in the same way as the picture signal from the G-channel.
The shift between the pulsated signals fed to the pulse comparator 12 corresponds to the off-set between the picture signal obtained at the G-channel image pickup system 1 and that yielded at the R-channel image pickup system 2. Thereafter, the control circuit 14 receives through the post-processing circuit 13 a signal from the pulse comparator 12, whereby to change the control signal which has been delivered to the registration correction unit 15 of the R-channel so that the pulsated signal input through the R-channel to the pulse comparator 12 coincides in timing with that fed as an input through the G-channel. The registration operation of the R-channel relative to the G-channel has now been automatically carried out.
Next, by turning the double throw switch 17 to the B-channel, the control signal to the registration correction unit 16 of the B-channel can be similarly changed and the registration operation of the B-channel relative to the G-channel is automatically carried out. Incidentally, use of a microcomputer as the control circuit 14 enables to perform all the above operations in accordance with a program stored in the microcomputer.
According to the autoregistration system depicted in FIG. 2, the registration can be readily readjusted in a short time period whenever needed and composite color television signals of excellent quality can be always obtained with accurate registration.
However, the prior art autoregistration system as shown in FIG. 2 requires a special optical pickup unit with the test pattern 5 built in exclusively for registration and, hence, it is accompanied by such drawbacks that the system tends to become voluminous and correspondingly costly.
In television cameras of the above system, their picture signals are field interlaced in most instances. The distance between each two adjacent scanning lines in each field is an integer times, for example, double that in each frame. Accordingly, the scanning lines in each field are relatively coarse. In order to carry out an registration operation in the vertical direction in the aforementioned autoregistration system, it is thus necessary to collect as samples picture signals along a desired vertical line in a section preselected at a central portion of the picture image and to perform the registration on the basis of the thus-sampled picture signals.
Accordingly, the registration in the vertical direction is carried out, in the above-mentioned autoregistration system, on the basis of picture signals on the relatively coarse scanning lines in each field. Although the above autoregistration system seems to promise sufficiently accurate operations, it is still accompanied by another drawback that it is difficult to obtain a sufficiently high level of registration accuracy in the vertical direction.